The present invention is related to freight brake control systems and particularly to a freight brake control system employing the conventional AB/D type brake control valve device, as fully shown and described in Westinghouse Air Brake Company Instruction Pamphlet G-g-5062-16.
Control valves of the above general type have traditionally operated during a brake application to connect the auxiliary reservoir pressure to the brake cylinder devices. In order to obtain higher braking pressure during an emergency brake application, in accordance with A.A.R. requirements, the emergency reservoir pressure is combined with the auxiliary reservoir pressure flowing to the brake cylinders. The A.A.R. specifies that the emergency reservoir pressures be in the order of 15%-20% higher than full service. In order to satisfy this regulation, the emergency reservoir has been designed to provide 3600 cubic inches of volume, which is relatively large by comparison with the 2500 cubic inch auxiliary reservoir, particularly in view of the fact that the additional brake pressure realized during emergency is only slightly higher than during a service application. A large volume emergency reservoir on each car of a train is not only expensive, but requires a considerable amount of space for mounting and takes considerable time to charge, thereby having the effect of extending the time required to release the brakes on cars near the end of a train.